Geographic Redundancy for Call Servers in a Cellular System Based on a Bearer-Independent Core Network

1. A method for transferring call control to a backup call server, comprising: transmitting call setup signals between a calling party mobile station and a Base Station Controller (BSC); transmitting call setup signals between the BSC and an originating Mobile Switching Center (MSC) and between the originating MSC and a gateway-MSC (G-MSC) by way of a first signaling gateway, and between the G-MSC and a Home Location Register (HLR), wherein the call setup signals are transmitted between the G-MSC and the HLR by way of a second signaling gateway, to determine a destination MSC; transmitting destination MSC information from the HLR to the G-MSC by way of the second signaling gateway; when the destination MSC fails, routing call setup signals received from the G-MSC to a backup MSC and establishing a call connection between the backup MSC and the originating MSC; when the G-MSC fails, routing the call setup signals received for the G-MSC to a backup G-MSC and establishing a call connection between the backup G-MSC and the originating MSC; and establishing a call connection between the calling party mobile station and a called party mobile station using at least one of the backup G-MSC and the backup MSC.

2. The method of claim 1 wherein the step of routing the call setup signals from the G-MSC to the backup MSC further comprises routing a first portion of the call setup signals from the G-MSC to a first backup MSC and a second portion of the call setup signals from the G-MSC to a second backup MSC, the backup MSC including the first backup MSC and the second backup MSC.

3. The method of claim 1 wherein the step of routing the call setup signals from the G-MSC to the backup MSC further comprises routing a first portion of the call setup signals to a first backup G-MSC and a second portion of the call setup signals to a second backup G-MSC, the backup G-MSC including the first backup G-MSC and the second backup G-MSC.

4. A cellular network, comprising: a Gateway Mobile Switching Station (G-MSC) for establishing call connections between originating MSCs and destination MSCs; a Home Location Register (HLR) for providing location information to the G-MSC as a part of call setup; a first signaling gateway within a plurality of signaling gateways coupled between each of a plurality of MSCs and the G-MSC; a second signaling gateway within the plurality of signaling gateways coupled between the G-MSC and the HLR; wherein the HLR identifies a destination MSC for a call being setup based upon a called party mobile station location record maintained in the HLR and transmits call signaling messages to the second gateway; wherein the second signaling gateway redirects the call signaling messages to a first backup G-MSC upon detecting that the G-MSC is in an inactive state; and wherein the first signaling gateway redirects the call signaling messages to a second backup G-MSC upon detecting that the G-MSC is in an inactive state.

5. The cellular network of claim 4 wherein the second gateway coupled between the G-MSC and the HLR comprises one of a plurality of signaling gateways.

6. The cellular network of claim 4 further comprising at least one signaling gateway coupled between the G-MSC and an originating MSC.

7. The cellular network of claim 4 further comprising at least one signaling gateway coupled between the G-MSC and the destination MSC.

8. The cellular network of claim 7 wherein at least one of the first and second backup G-MSC also operates as a primary G-MSC.

9. A signaling gateway for a cellular network coupled to communicate with a destination switching element and to at least one home location register (HLR), comprising: a processor; a memory for storing computer instructions that define the operational logic of the signaling gateway, wherein the computer instructions include logic for: receiving call signaling messages from the at least one HLR or an initiating Mobile Switching Station (MSC); determining whether the destination switching element is in an inactive state; if the destination switching element is in an inactive state, determining a first-backup switching element; transparently forwarding the call signaling messages to the first backup switching element; and determining a second backup switching element and forwarding a first group of call signaling messages to the first backup switching element and forwarding a second group of call signaling messages to the second backup switching element.